As various environmental problems have occurred due to use of fossil fuel and an increase in carbon dioxide in the air, the development of an alternative energy source has been required. Solar energy is a continuous and infinite energy source, and since solar energy supplied to the earth for 1 hour may meet energy consumed in the world for a year, a method of converting solar energy into usable fuel may provide an ultimate solution for solving an energy depletion problem.
Microalgae, which are organisms capable of converting more than half of 120 TW supplied from the sun into a useful energy source such as biomass, lipid, or the like, through biosynthesis, has been spotlighted as a novel energy source. However, there is a limitation in converting infinite solar energy due to low photosynthetic efficiency of photosynthetic organisms itself. Theoretical maximum photosynthetic efficiency is 8 to 10% under continuous light conditions, but actually, it is difficult to achieve the maximum photosynthetic efficiency due to flexible light intensity and an inhibition action of strong light on photosynthesis. Therefore, at the time of mass cultivation of microalgae, cells existing on a surface of a reactor are subjected to a photo-oxidative damage by strong light, and photo-energy transferred to cells existing inside the reactor receives is small, such that the cells existing inside the reactor is subjected to photosynthesis inhibition, which decreases photo-energy conversion efficiency by at most 95%. Therefore, in order to improve productivity in a process of utilizing photosynthetic organisms, it is essential to adjust a balance between absorbing photo-energy and using the photo-energy.
As one of the methods of improving photosynthetic efficiency of the microalgae, a method of decreasing a chlorophyll antenna size has been used. 100 or more genes participate in and regulate photosynthesis mechanism, which is one of the most complicated biochemical mechanisms, and a large number of proteins and coenzymes are required for an electron transport system, carbon dioxide fixation, and synthesis of photosynthetic pigments. Therefore, the method of improving photosynthetic efficiency through a method of inhibiting chlorophyll b synthesis to decrease the antenna size is insufficient as an ultimate solution, such that a more efficient selection method is required.
The microalgae evolutionally have phototaxis to sense directionality with respect to light stimulation and move toward a desired position at the same time. In the case in which the microalgae do not have phototaxis, a photodamage or photosynthesis inhibition phenomenon may occur with respect to various light stimulations. Therefore, regulation of phototaxis in the microalgae may be considered as one of the main factors for optimal photosynthesis.
Therefore, the present inventors tried to select strains having a rapid cell growth property and excellent lipid productivity as compared to existing wild-type strains, and confirmed that in the case of selecting strains having excellent phototaxis with respect to light at a cellular level using phototaxis of microalgae, strains having improved photosynthetic efficiency and growth property may be easily and efficiently secured, thereby completing the present invention.